The BASIC-command CLOSE is used for closing opened files or drive numbers, so that the data can be written from the write buffer on tape or disk. If CLOSE is omitted after opening a file, the data of the file can be incomplete or unreadable. As a rule, CLOSE should be used whenever any of the BASIC-commands CMD, GET#, INPUT# or PRINT# has been used, but no further file access is needed anymore.

The numerical values from 0 to 255 are valid logical file numbers. Beyond that range - with negative values or values greater than 255 - the BASIC-error "?ILLEGAL QUANTITY ERROR IN" line occurs.